All the types of substitution which apply to major keys (relative substitutions, scale tone triads or 7ths two degrees ahead in the key, dominant minor, and tritone substitutions) can be applied to minor keys as well. The main difference you will find is that when you start to go into the upper extensions of chords built on the harmonic and melodic minors, you will get alterations to the chords. Shown here are the chords resulting from substituting scale tone 7th chords two ahead for the standard scale tone 7ths of A melodic minor.
Here is a Latin Jazz style piece in A minor featuring extended chords. Learn it and then try improvising with the chords and phrasing. If you intend to play much Jazz, it is recommended that you jam with other musicians as often as possible, as interaction and improvisation are central to Jazz, and the human interaction is the most essential element in all music.
This piece by Bartok contains several time signature changes and may look difficult but it has a natural rhythmic flow to it. You could write it down and put counting numbers under the notes, but a better way to learn this kind of piece is to learn the feel of the rhythm and phrasing by playing it many times.